Guess how slim Robert Pattinson got for his role in The Lost City Of Z

To play an explorer swallowed up by the untold dangers of the Amazon, Robert Pattinson adopted a diet so intense that his body was fit for some curve-hugging denim.

Pattinson told PEOPLE at The Lost City of Z premiere, Saturday, that he and his cast-mates had lived on as little as one meal a day while portraying 1920s adventurers who disappeared into the Brazilian jungle while searching for the infamous City of Z.

“I had literally eaten nothing for the entire time,” he explained of his dietary restrictions for the role, adding, “I loved it afterwards, for like a week in London, where I have a 28-inch waist. I was like, ‘Ooh! Skinny jeans!’ ”

Robert Pattinson at the Closing Night Screening of 'The Lost City Of Z' in New York on October 15.

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The actor, 30, said he quickly returned to a more healthy form, because “after six or seven weeks of just eating half a little tiny bit of fish and like a crumb of rice, and then you eat a sandwich and you’ve got on 15 pounds afterward.”

Edward Ashley told PEOPLE at the Lincoln Center premiere that the weight loss was a team effort, with Charlie Hunnam leading the charge.

“We had to lose a lot of weight and we’d work out every night together, we’d box and we’d stay to the diet together,” shared Ashley. “We’d eat, like, an egg for breakfast. An avocado and some tuna for lunch. And then that was it.”